You seein' dis?
— The Scout spectating an intense round
SourceTV is a mechanic of several Source Engine games, including Team Fortress 2, which offers the ability to have an unlimited number of spectators watching online games based on the Source Engine. The camera view is controlled by an auto-director AI or a human cameraman. SourceTV spectators are invisible to players and can't interact with the running game in any way.
SourceTV has been patched many times since its inception with the game, although much of its purpose has been overtaken by streaming services like Twitch and YouTube livestreams in recent years.